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PubMed1998

Mismatch G-T binding activity and MSH2 expression is quantitatively related to sensitivity of cells to methylating agents.

To elucidate mechanisms involved in alkylating drug resistance, Chinese hamster cells resistant to methylating agents have been generated upon transfection with human DNA. Here it is shown that these Chinese hamster ovary (CHO) variants exhibit the tolerance phenotype: they are alkyltransferase deficient (Mex-), cross-resistant to 6-thioguanine, exhibit reduced G-T binding (MutS alpha) activity and express the mismatch repair protein MSH2 at a significantly lower level than the corresponding control. By comparing wild-type cells with different tolerant strains that show gradual differences in resistance to methylating agents, it was shown that both the G-T binding activity and the amount of MSH2 protein inversely correlates with the level of methylating drug resistance. Although the tolerant cell variants analysed express MSH2 at a significantly lower level than the wild-type, MSH2 mRNA expression was not impaired. Furthermore, MSH2 promoter activity was not reduced upon transient transfection into tolerant cells. The results indicate that quantitative differences in expression of components of mismatch repair do exist in mammalian cells that affect cell survival upon methylation. It appears that post-transcriptional mechanisms are involved in regulation of MSH2 expression.

Alkylating Agents↗
PubMed2005

MSH2 missense mutations alter cisplatin cytotoxicity and promote cisplatin-induced genome instability.

Defects in the mismatch repair protein MSH2 cause tolerance to DNA damage. We report how cancer-derived and polymorphic MSH2 missense mutations affect cisplatin cytotoxicity. The chemotolerance phenotype was compared with the mutator phenotype in a yeast model system. MSH2 missense mutations display a strikingly different effect on cell death and genome instability. A mutator phenotype does not predict chemotolerance or vice versa. MSH2 mutations that were identified in tumors (Y109C) or as genetic variations (L402F) promote tolerance to cisplatin, but leave the initial mutation rate of cells unaltered. A secondary increase in the mutation rate is observed after cisplatin exposure in these strains. The mutation spectrum of cisplatin-resistant mutators identifies persistent cisplatin adduction as the cause for this acquired genome instability. Our results demonstrate that MSH2 missense mutations that were identified in tumors or as polymorphic variations can cause increased cisplatin tolerance independent of an initial mutator phenotype. Cisplatin exposure promotes drug-induced genome instability. From a mechanistical standpoint, these data demonstrate functional separation between MSH2-dependent cisplatin cytotoxicity and repair. From a clinical standpoint, these data provide valuable information on the consequences of point mutations for the success of chemotherapy and the risk for secondary carcinogenesis.

Amino Acid Sequence↗
PubMed2003

[Is immunohistochemistry for MLH1 and MSH2 proteins a useful method for detection of microsatellite instability in sporadic colorectal cancer?].

BACKGROUND/AIMS: In order to identify microsatellite instability (MSI), the test based on the polymerase chain reaction (PCR) can be used. However, PCR is not routinely performed in all hospital laboratories. Recently, immunohistochemistry (IHC) for MLH1 and MSH2 proteins has been reported as a rapid and useful method for MSI. However, the efficacy of IHC in the detection of the MSI has not been well established. The aim of this study was to evaluate the usefulness of IHC in the detection of the MSI by comparing it with the test results using PCR in colorectal cancer (CRC). METHODS: Paraffin-embedded normal and tumor tissues from seventy-five patients who underwent surgical resection of CRC were used. Abnormal expression of MLH1 and MSH2 protein was determined by IHC using MLH1 and MSH2 antibodies. Normal and tumor DNAs were obtained from thirty CRC tissues that showed abnormal expression of MLH1 and MSH2 proteins by IHC. The MSI status was confirmed by PCR using five markers. RESULTS: Thirty tumors showed abnormal expression of MLH1 and MSH2 proteins by IHC, but only three tumors out of them were confirmed to have MSI by PCR. CONCLUSIONS: This result suggests that IHC with MLH1 and MSH2 antibodies does not seem to be a useful method to identify MSI in CRC, therefore PCR is required for detection of the MSI.

Adaptor Proteins, Signal Transducing↗
PubMed2004

[Abnormal expression of fragile histidine triad (FHIT) and Mut S homolog 2 (MSH2) proteins in human sporadic colorectal carcinoma and their clinical significance].

BACKGROUND & OBJECTIVE: Frequent loss of fragile histidine triad (FHIT) expression in human gastrointestinal tract carcinomas has been reported; however, there were divergent opinions regarding FHIT expression in colorectal carcinoma. Recent studies have suggested that FHIT inactivation can be a consequence of defects in mismatch repair proteins, particularly mut S homolog 2 (MSH2). This study was designed to investigate the expression and clinical significance of FHIT and MSH2 proteins in human sporadic colorectal carcinoma (SCC). METHODS: Immunohistochemistry SP method was used to determine the expression of FHIT and MSH2 in surgically resected specimens of 84 SCC and its corresponding paratumor normal colorectal tissues, and 23 cases of colonic adenomas. RESULTS: The positive expression rates of FHIT protein were 48.81%, 73.91%, and 100% in SCC, colonic adenomas, and adjacent normal colorectal tissues, respectively. The positive expression rates of FHIT protein showed increasing trend from SCC, colonic adenomas, to paratumor normal colorectal tissues; and the difference was statistically significant (P< 0.05). The expression levels of FHIT were not associated with age, gender, tumor site, and histological type (P >0.05), but were correlated with tumor invasive depth, differentiation degree, Dukes,stage, and lymph node metastasis (P< 0.05). The tumor tissues of deeper invade depth, lower differentiation degree, later Ducks,stage and with lymph node metastasis showed more reduction of FHIT protein expression. The expression level of MSH2 was only related to Dukes, stage (P< 0.05). FHIT expression was closely associated with MSH2 expression in SCC (r=0.3728,P< 0.01). CONCLUSION: (1) Loss or reduction of FHIT protein expression plays an important role in the development and progression of SCC. The expression levels of FHIT protein are related to the malignant degree of SCC and may be a valuable biological indicator for predicting the potent invasion and metastasis of SCC. (2) FHIT protein expression is in a positive correlation fashion with MSH2 protein expression in SCC.

Acid Anhydride Hydrolases↗
PubMedDate not supplied

Altered expression and new mutations in DNA mismatch repair genes MLH1 and MSH2 in melanoma brain metastases.

Brain metastases, including those of malignant melanoma (known for its high genomic instability), are the most common intracranial tumors. The main objective of this study was to investigate expression and mutation in the DNA mismatch repair system in melanoma brain metastases. Expression of MLH1, MSH2, PMS1 and PMS2 was investigated immunohistochemically in 31 melanoma metastatic tumors. Mutational analysis of MLH1 and MSH2 was performed in 17 melanoma brain metastases. Loss of MLH1 and MSH2 expression was found in 10/31 and 12/31 tumors. PMS1 (27/31) and PMS2 (28/31) expression was preserved in the majority of lesions. Potential missense mutation was found in MSH2 (exon 13) in 2/17 melanomas. Mutation in the intron sequence between exon 14 and 15 of MLH1 (exon 15) was observed in 4/17 cases. Our results indicate that the two major DNA mismatch repair genes, MLH1 and MSH2, are more frequently affected by alterations in the DNA mismatch repair system than the helper genes PMS1 and PMS2. The presence of mutations of MSH2 and MLH1 in melanoma brain metastases, which has not been found in primary melanomas, indicates the high genomic instability of melanoma brain metastases.

Adaptor Proteins, Signal Transducing↗
PubMed2004

Immunohistochemistry and microsatellite instability testing for selecting MLH1, MSH2 and MSH6 mutation carriers in hereditary non-polyposis colorectal cancer.

Hereditary non-polyposis colorectal cancer (HNPCC) represents 1-3% of all colorectal cancers. HNPCC is caused by a constitutional defect in a mismatch repair (MMR) gene, most commonly affecting the genes MLH1, MSH2 and MSH6. The MMR defect results in an increased cancer risk, with the greatest lifetime risk for colorectal cancer and other cancers associated to HNPCC. The HNPCC-associated tumor phenotype is generally characterized by microsatellite instability (MSI) and immunohistochemical loss of expression of the affected MMR protein. The aim of this study was to determine the sensitivity of IHC for MLH1, MSH2 and MSH6, and MSI analysis in tumors from known MMR gene mutation carriers. Fifty-eight paired normal and tumor samples from HNPCC families enrolled in our high-risk colorectal cancer registry were studied for the presence of germline mutations in MLH1, MSH2 and MSH6 by DGGE and direct sequencing. MSI analysis and immunostaining for MLH1, MSH2 and MSH6 were evaluated. Of the 28 patients with a real pathogenic mutation, loss of immunohistochemical expression for at least 1 of these MMR proteins was found, and all except 1 have MSI-H. Sensitivity by MSI analysis was 96%. IHC analysis had a sensitivity of 100% in detecting MMR deficiency in carriers of a pathogenic MMR mutation, and can be used to predict which gene is expected to harbor the mutation for MLH1, MSH2 and MSH6. This study suggests that both analyses are useful for selecting high-risk patients because most MLH1, MSH2 and MSH6 gene carriers will be detected by this 2-step approach. This practical method should have immediate application in the clinical work of patients with inherited colorectal cancer syndromes.

Adaptor Proteins, Signal Transducing↗
PubMed2005

[The first molecular analysis of a Hungarian HNPCC family: a novel MSH2 germline mutation].

BACKGROUND: Hereditary nonpolyposis colorectal cancer is an inherited disease characterized by onset at an early age, an excess of synchronous and metachronous large bowel tumors and a variety of extracolorectal malignancies. Basal and squamous cell carcinomas of the skin are not customarily included in the tumor spectrum of the syndrome. The disease is caused by a germline mutation in one of the DNA mismatch repair genes, most commonly MSH2 or MLH1, and typically presents with microsatellite instability and frequent loss of mismatch repair protein expression in the tumor tissue. PATIENT: The case of a 62-year old woman who had a history of colon cancer at the age of 46 years, endometrial cancer at the age of 56 years, baso-squamous, and squamous cell cancer of the face at the ages of 53, 54, 62 and 58 years, respectively, and rectal cancer at 60 is reported. Her family fulfills the Amsterdam criteria for the diagnosis of hereditary nonpolyposis colorectal cancer. The baso-squamous cell, the squamous cell, the endometrial and the rectal cancers were assessed for the microsatellite instability status and the expression of the MSH2 and MLH1 mismatch repair proteins, and the p53 tumor suppressor protein by immunohistochemistry. Mutational screening using an automated capillary DNA sequencer was performed by the direct genomic sequencing of 17 fragments of the MSH2 gene, which covers promoter, all exons and flanking intronic regions. RESULTS: All cancers displayed microsatellite instability and were positive for the p53 protein. The immunohistochemical staining in the baso-squamous cell, the squamous cell, the rectal and endometrial cancers were negative for MSH2 and positive for MLH1 proteins. DNA sequencing analysis revealed a mutation c.2292G > A in exon 14 of the MSH2 gene, which is altering the 764. amino acid, the tryptophan to STOP codon (p.W764X). Thus the MSH2 protein is presumably truncated by 171 aminoacids. CONCLUSION: To the best of authors' knowledge, this is the first molecular characterization of a Hungarian hereditary nonpolyposis colorectal cancer family. According to the Human Mutation Database and International Collaborative Group of HNPCC Database, this mutation is novel, has not been reported previously. Cutaneous baso-squamous and squamous cell cancers may present as part of the HNPCC phenotype. Detection of the loss of mismatch repair protein expression and mismatch repair gene mutation mapping, represents a significant improvement of the diagnosis of this syndrome in Hungary. These examinations identify the mutation carriers who are at an increased risk of developing cancers.

Adaptor Proteins, Signal Transducing↗
PubMed2005

The analysis for identifying large DNA fragment aberrations of MSH2 and MLH1 genes from familial colorectal cancer in China.

OBJECTIVE: To investigate the frequency of large fragment aberrations of MSH2 and MLH1 genes from Chinese colorectal cancer (CRC) patients with family history. METHODS: Sixteen exons of MSH2, nineteen exons of MLH1 and seven DNA sequences from the other genes of the samples were screened and checked by multiplex ligation dependent probe amplification (MLPA). First, the methodology was confirmed by testing the positive and negative control samples. Then, 32 CRC or hereditary nonpolyposis colorectal cancer (HNPCC) patients with family history and 20 cases of sporadic CRC were applied to investigate for the large fragment aberrations of MSH2 and MLH1 genes. RESULTS: The genomic DNA fragment deletions of all positive controls were identified and verified by MLPA. Three cases of 32 familial (hereditary) CRC/HNPCC were detected and identified to be the germline heterozygous deletions of MSH2 gene, of which exons 1-7 were deleted from patient No.3, exon 11 from No.25 and exons 2-6 from No.11. However, no genomic DNA fragment aberration of either MSH2 or MLH1 gene was uncovered from 20 sporadic CRC. CONCLUSION: Large DNA fragment aberrations of MSH2 gene was a frequent cause of Chinese HNPCC and CRC patients with family history, and the identification of those aberrations should be included in the regular genetic analysis for CRC/HNPCC patients.

Adaptor Proteins, Signal Transducing↗
PubMed1996

Genetic counseling in hereditary nonpolyposis colorectal cancer: an extended family with MSH2 mutation.

OBJECTIVES: Molecular genetic advances have increased the demand for DNA testing. We describe DNA based genetic counseling in a hereditary nonpolyposis colorectal cancer (HNPCC) family. METHODS: This extended HNPCC family was found to harbor the MSH2 germline mutation. Family history, medical, and pathology documents enabled us to secure a high degree of verification that the kindred qualified as HNPCC. DNA testing revealed the MSH2 germline mutation that was verified independently in two laboratories. Genetic counseling was provided before DNA testing and disclosure of MSH2 findings. RESULTS: Genetic counseling revealed a variety of findings characterized by emotional stress in MSH2 germline mutation carriers. Concerns centered around reproductive issues, potential transmission of the deleterious gene to their progeny, and discrimination by insurance carriers and employers. More than one-half of the patients found to harbor the MSH2 mutation considered the option of prophylactic subtotal colectomy. CONCLUSION: DNA testing should be restricted to well-verified candidate families in which genetic counseling should be mandatory. HNPCC family members sought genetic risk assessment for their own health and that of their children. Contrasting emotional responses took place when told of their gene testing status and this required a sensitive empathetic listening ear. Patients have many concerns about their lifetime cancer destiny when told that they harbor the culprit MSH2 germline mutation.

Adult↗
PubMed1997

Mutations in MLH1 are more frequent than in MSH2 in sporadic colorectal cancers with microsatellite instability.

The microsatellite instability that is a feature of tumors in patients with hereditary nonpolyposis colorectal cancer (HNPCC) is a consequence of defective DNA mismatch repair. Mutations in the DNA mismatch repair genes MSH2 and MLH1 may account for up to 90% of HNPCC kindreds. Microsatellite instability is also seen in 10-16% of sporadic colorectal cancers. A limited number of MSH2 and MLH1 mutations have been described for sporadic colorectal cancers. In this study, we screened 12 primary sporadic colorectal cancers with microsatellite instability for mutations in MSH2 and MLH1 by using reverse transcription-polymerase chain reaction (RT-PCR) and single-strand-conformation-variant (SSCV) analysis. Eight mutations were identified in six tumors. One mutation in MLH1 was found to be present in the patient's germline DNA. Four tumors had somatic mutations in MLH1, and, in two of these tumors, two different mutations were identified. A single tumor had a somatic MSH2 mutation. Our observations suggest that MLH1 is mutated more frequently than MSH2 in sporadic colorectal cancers with microsatellite instability.

Adaptor Proteins, Signal Transducing↗
PubMed2006

A novel MSH2 germline mutation in homozygous state in two brothers with colorectal cancers diagnosed at the age of 11 and 12 years.

Hereditary non-polyposis colorectal cancer (HNPCC) syndrome is caused by heterozygous germline mutations in DNA mismatch repair genes (MMR), (MSH2, MLH1, MSH6, and PMS2) and it is inherited in an autosomal dominant pattern with high penetrance. Several patients have been reported carrying bi-allelic MMR gene mutations and whose phenotype resembled a syndrome with childhood malignancies including hematological malignancies, brain, and colorectal tumors. This phenotype is similar to the tumor spectrum of MMR knockout mice. Herein we describe two brothers of healthy consanguineous parents from Pakistan, who had developed two and three colorectal cancers at the ages of 11 and 12 years, respectively, and less than 30 polyps. Tumor specimens were microsatellite instable (MSI-H), and expression of MSH2 and MSH6 was lost. Mutation analyses of DNA samples from both patients revealed a novel homozygous c.2006-5T > A mutation in intron 12 of the MSH2 gene. This phenotype of the brothers is unusual as they neither develop hematological malignancies nor brain tumors at an older age of presentation than other patients with homozygous MSH2 mutations. The milder phenotype may be due to the expression of low amounts of MSH2 protein with reduced activity.

Child↗
PubMed2003

Microsatellite instability and expression of MLH1 and MSH2 in carcinomas of the small intestine.

BACKGROUND: Carcinomas of the small intestine are rare, but the risk is greatly increased in patients with hereditary nonpolyposis colorectal cancer (HNPCC) due to an inherited mismatch repair (MMR) gene mutation, most commonly affecting the genes MLH1 or MSH2. Defective MMR is characterized by microsatellite instability (MSI) and loss of MMR protein expression in the tumor tissue. However, a subset of several sporadic tumor types, including about 15% of colon cancers, also evolve through defective MMR. METHODS: The authors have assessed the frequency of MSI and analyzed the immunohistochemical expression of MLH1 and MSH2 in a population-based series of 89 adenocarcinomas of the small intestine. To study the contribution of MSI and defective MMR protein expression in young patients, 43 cancers of the small intestine from patients below age 60 years (including 24 tumors from the population-based series and an additional 19 tumors from young individuals) were also analyzed. RESULTS: MSI was detected in 16/89 tumors (18%) in the population-based series, and immunohistochemistry revealed loss of expression for MLH1 in 7/16 MSI tumors and in 2/73 MSS tumors, whereas all tumors showed normal expression for MSH2. Among the young patients, the authors identified MSI in 10/43 tumors (23%), and 6 of these 10 MSI tumors showed immunohistochemical loss of MMR protein expression, which affected MLH1 in 3 cases and MSH2 in 3 cases. CONCLUSIONS: The frequency of MSI (18%) in adenocarcinomas of the small intestine equals that of colon cancer. However, silencing of MLH1 seems to explain the MSI status in only about half of the MSI tumors. Among patients with cancer of the small intestine before age 60 years, MSI is found in 23% of the cases, with MLH1 and MSH2 being affected at equal frequencies, indicating that HNPCC may underly a subset of such cases.

Adaptor Proteins, Signal Transducing↗
PubMed2005

Molecular characterization of the spectrum of genomic deletions in the mismatch repair genes MSH2, MLH1, MSH6, and PMS2 responsible for hereditary nonpolyposis colorectal cancer (HNPCC).

A systematic search by Southern blot analysis in a cohort of 439 hereditary nonpolyposis colorectal cancer (HNPCC) families for genomic rearrangements in the main mismatch repair (MMR) genes, namely, MSH2, MLH1, MSH6, and PMS2, identified 48 genomic rearrangements causative of this inherited predisposition to colorectal cancer in 68 unrelated kindreds. Twenty-nine of the 48 rearrangements were found in MSH2, 13 in MLH1, 2 in MSH6, and 4 in PMS2. The vast majority were deletions, although one previously described large inversion, an intronic insertion, and a more complex rearrangement also were found. Twenty-four deletion breakpoints have been identified and sequenced in order to determine the underlying recombination mechanisms. Most fall within repetitive sequences, mainly Alu repeats, in agreement with the differential distribution of deletions between the MSH2 and MLH1 genes: the higher number and density of Alu repeats in MSH2 corresponded with a higher incidence of genomic rearrangement at this disease locus when compared with other MMR genes. Long interspersed nuclear element (LINE) repeats, relatively abundant in, for example, MLH1, did not seem to contribute to the genesis of the deletions, presumably because of their older evolutionary age and divergence among individual repeat units when compared with short interspersed nuclear element (SINE) repeats, including Alu repeats. Moreover, Southern blot analysis of the introns and the genomic regions flanking the MMR genes allowed us to detect 6 novel genomic rearrangements that left the coding region of the disease-causing gene intact. These rearrangements comprised 4 deletions upstream of the coding region of MSH2 (3 cases) and MSH6 (1 case), a 2-kb insertion in intron 7 of PMS2, and a small (459-bp) deletion in intron 13 of MLH1. The characterization of these genomic rearrangements underlines the importance of genomic deletions in the etiology of HNPCC and will facilitate the development of PCR-based tests for their detection in diagnostic laboratories.

Adaptor Proteins, Signal Transducing↗
PubMed2002

A modified multiplex PCR assay for detection of large deletions in MSH2 and MLH1.

A method for detection of large genomic deletions in the MSH2 and MLH1 genes based on multiplex PCR and quantitative evaluation of PCR products is presented. All 35 exons of MSH2 and MLH1 were screened simultaneously in seven PCR reactions, each of them including primers for both genes. The method is reliable for uncovering large genomic deletions in patients suspected of HNPCC. With this method, six novel deletions were identified, two in MSH2: EX1_10del and EX1_16del (representing deletion of the entire MSH2 gene); and four in MLH1: EX1_10del in two unrelated patients, EX3_5del, and EX4del. The deletions were detected in 18 unrelated patients in whom no germline mutation had been identified by SSCP and DHPLC. These results indicate that our modified multiplex PCR assay is suited for the detection of large deletions both in the MSH2 and MLH1 gene and therefore represents an additional valuable tool for mutation screening in HNPCC families.

Adaptor Proteins, Signal Transducing↗
PubMed2005

The 5' region of the MSH2 gene involved in hereditary non-polyposis colorectal cancer contains a high density of recombinogenic sequences.

MSH2 rearrangements are involved in approximately 10% of hereditary non-polyposis colorectal cancer (HNPCC) families, and in most of the rearrangements, exon 1 is deleted. We scanned by quantitative multiplex polymerase chain reaction (PCR) of short fluorescent fragments (QMPSF) 200 kb of genomic sequences upstream of the MSH2 transcription initiation site in 21 HNPCC families with exon 1 deletions. This QMPSF scan revealed 12 distinct 5' breakpoints located up to 200 kb upstream of the MSH2 transcription initiation site. Sequencing analysis of the rearranged allele in 17 families revealed that most of the deletions (15/17) resulted from homologous Alu-mediated recombination. QMPSF and sequencing analysis in these 21 families led us to detect the presence of 20 distinct 5' breakpoints. In 14 out of 15 Alu-mediated recombinations, we found, either within the identical region in which the recombination had probably occurred or in its vicinity, the 26-bp Alu core sequence containing the recombinogenic Chi-like motif. Compared to the equivalent regions of other human genes, the MSH2 upstream region was found to contain a high density of Alu repeats (30% within 228 kb and 43% within 50 kb), most of which belong to the old Alu S subfamilies. In conclusion, this study demonstrates the heterogeneity of the breakpoints within the MSH2 upstream region and reveals the remarkable density of recombinogenic Alu sequences in this region.

Adult↗
PubMed2006

Distinct patterns of germ-line deletions in MLH1 and MSH2: the implication of Alu repetitive element in the genetic etiology of Lynch syndrome (HNPCC).

A relatively high frequency of germ-line genomic rearrangements in MLH1 and MSH2 has been reported among Lynch Syndrome (HNPCC) patients from different ethnic populations. To investigate the underlying molecular mechanisms, we characterized the DNA breakpoints of 11 germ-line deletions, six for MLH1 and five for MSH2. Distinct deletion patterns were found for the two genes. The five cases of MSH2 deletions result exclusively from intragenic unequal recombination mediated by repetitive Alu sequences. In contrast, five out of the six MLH1 deletions are due to recombinations involving sequences of no significant homology (P=0.015). A detailed analysis of the DNA breakpoints in the two genes, previously characterized by other groups, validated the observation that Alu-mediated unequal recombination is the main type of deletion in MSH2 (n=34), but not in MLH1 (n=21) (P<0.0001). Plotting the distribution of known DNA breakpoints among the introns of the two genes showed that, the highest breakpoint density is co-localized with the highest Alu density. Our study suggests that Alu is a promoting factor for the genomic recombinations in both MLH1 and MSH2, and the local Alu density may be involved in shaping the deletion pattern.

Adaptor Proteins, Signal Transducing↗
PubMed2002

Prevalence of germline mutations of MLH1 and MSH2 in hereditary nonpolyposis colorectal cancer families from Spain.

HNPCC is an autosomal dominantly inherited cancer-susceptibility syndrome that confers an increased risk for colorectal cancer and endometrial cancer at a young age. It also entails an increased risk of a variety of other tumors, such as ovarian, gastric, uroepithelial and biliary tract cancers. The underlying pathogenic mutation lies in 1 of the 5 known DNA MMR genes (MSH2, MLH1, PMS1, PMS2 and MSH6). We screened a total of 140 individuals from 56 Spanish families with suspected HNPCC for mutations in the DNA mismatch repair genes MLH1 and MSH2, using DGGE and direct DNA sequencing. Families were selected on the basis of a history of HNPCC-related tumors or the occurrence of other associated tumors in members besides the index case affected with colorectal cancer. We detected 14 definite pathogenic germline mutations, 9 in MLH1 and 5 in MSH2 in 13 unrelated families selected by the Amsterdam criteria and Bethesda guidelines (1 family carries 2 mutations) and 3 missense mutations in 3 unrelated families selected by the Amsterdam criteria. Among the 17 germline mutations noted in the Spanish cohort, 10 are novel, 7 in MLH1 and 3 in MSH2, perhaps demonstrating different mutational spectra in the Spanish population, where no founder mutation has been identified. Based on our results, we suggest that in the Spanish population not only HNPCC families fulfilling the Amsterdam criteria but also those following Bethesda guidelines should undergo genetic testing for MSH2 and MLH1 mutations.

Adaptor Proteins, Signal Transducing↗
PubMed2005

Spectrum and frequencies of mutations in MSH2 and MLH1 identified in 1,721 German families suspected of hereditary nonpolyposis colorectal cancer.

Mutations in DNA MMR genes, mainly MSH2 and MLH1, account for the majority of HNPCC, an autosomal dominant predisposition to colorectal cancer and other malignancies. The evaluation of many questions regarding HNPCC requires clinically and genetically well-characterized HNPCC patient cohorts of reasonable size. One main focus of this multicenter study is the evaluation of the mutation spectrum and mutation frequencies in a large HNPCC cohort in Germany; 1,721 unrelated patients, mainly of German descent, who met the Bethesda criteria were included in the study. In tumor samples of 1,377 patients, microsatellite analysis was successfully performed and the results were applied to select patients eligible for mutation analysis. In the patients meeting the strict Amsterdam criteria (AC) for HNPCC, 72% of the tumors exhibited high microsatellite instability (MSI-H) while only 37% of the tumors from patients fulfilling the less stringent criteria showed MSI-H; 454 index patients (406 MSI-H and 48 meeting the AC of whom no tumor samples were available) were screened for small mutations. In 134 index patients, a pathogenic MSH2 mutation, and in 118 patients, a pathogenic MLH1 mutation was identified (overall detection rate for pathogenic mutations 56%). One hundred sixty distinct mutations were detected, of which 86 are novel mutations. Noteworthy is that 2 mutations were over-represented in our patient series: MSH2,c.942+3A>T and MLH1,c.1489_1490insC, which account for 11% and 18% of the MSH2 and MLH1 mutations, respectively. A subset of 238 patients was screened for large genomic deletions. In 24 (10%) patients, a deletion was found. In 72 patients, only unspecified variants were found. Our findings demonstrate that preselection by microsatellite analysis substantially raises mutation detection rates in patients not meeting the AC. As a mutation detection strategy for German HNPCC patients, we recommend to start with screening for large genomic deletions and to continue by screening for common mutations in exon 5 of MSH2 and exon 13 of MLH1 before searching for small mutations in the remaining exons.

Adaptor Proteins, Signal Transducing↗